This invention relates to a novel heat-resistant synthetic resin composition and to a method for the manufacture thereof.
For insulated wires, varnishes, films, laminated sheets, impregnating resins, adhesive agents, etc. which are used in electric appliances, generally phenolic resin, polyvinyl formal resin, polyester resin, alkyd resin, epoxy resin, polyester imide resin, polyamide imide resin, and polyimide resin are adopted.
In recent years, the increasing trend of electric appliances toward enhanced performance and decreased size has encouraged the appreciation of the importance of organic materials such as polyamide imide resin and polyimide resin which enjoy excellent heat resistance.
In the field of insulating varnishes, polyester resin varnishes which have heretofore found rather, widespread at acceptance on account of well-balanced combinations of heat resistance, mechanical properties, electric properties, and economics have come to be replaced in the recent years by varnishes of imide group-containing resins such as polyester imide, polyamide imide, and polyimide resins which offer higher heat resistance.
It is known that among imide group-containing resins, the polyamide imide resin enjoys the best balance of heat resistance, mechanical properties, electric properties, and chemical properties.
The conventional aromatic polyamide imide resin, however, has a disadvantage that the varnish of this resin becomes expensive because this resin is barely soluble in very costly organic polar solvents such as N-methyl-2-pyrrolidone and dimethylacetamide.
Further any varnish which uses an organic polar solvent has a disadvantage that the storage of the varnish itself and the handling of the varnish during its actual use are both very difficult because the organic polar solvent has strong hygroscopicity.
To avoid the trouble, there has been developed a polyamide imide resin having improved solubility in organic solvents by using a specific diamine or diisocyanate as part of the raw materials (U.S. Pat. No. 3,696,077).
Since this polyamide imide resin necessitates use of a specific aromatic diamine or diisocyanate, it has a disadvantage that the properties cannot be balanced easily and the cost of raw materials is high.